1. Field of the Invention
The invention is related to the field of solid-state memories and, in particular, to a magnetic memory comprised of a three-dimensional stack of layers. More particularly, embodiments of the invention describe read/write elements for the three-dimensional magnetic memory.
2. Statement of the Problem
Solid-state memory is a nonvolatile storage medium that uses no moving parts. Some examples of solid-state memory are flash memory and MRAM (magnetoresistive random access memory). Solid-state memories provide advantages over conventional disk drives in that data transfers to and from solid-state memories take place at a much higher speed than is possible with electromechanical disk drives. Solid-state memories may also have a longer operating life and may be more durable due to the lack of moving parts.
Solid state memories are typically fabricated as a two-dimensional array of memory cells, also referred to as cross-point memory arrays. The memory cells may be formed from Magnetic Tunnel Junction (MTJ) devices or other types of semiconductor devices. To form the cross-point memory array, the array of memory cells is sandwiched between bit lines (i.e., conductors) on one side, and word lines on the other side which are situated orthogonal to the bit lines. To write to a memory cell, current is passed down the bit line and the word line which contact the memory cell. The current on the bit line and the word line are able to switch the state of the memory cell from a logical “1” to a logical “0” or vice versa. To read from the memory cell, current over the word line and/or the bit line are sensed to determine the present state of the memory cell.
One problem with traditional solid-state memories is that storage capacity is much less than can be achieved with electromechanical disk drives. For instance, a common flash memory may store up to approximately 1 gigabyte (GB), whereas a common hard drive may store up to 100 GB or more. Also, the cost per megabyte is higher for solid-state memories than for electromechanical disk drives. Thus, it would be desirable to fabricate or develop solid-state memories that have larger storage capacities.